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Why do "strict acceptor checking"?

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Twice this week I have helped other sites deal with issues related to
"strict acceptor checking" (the programs in question were sshd and
sudo).  Both of these programs explicitly have code that constructs a
service name based on the value of gethostname() and thus will only
accept a service ticket for that name regardless of what's actually
in the keytab, and this fails in a number of complicated multihomed
networking situations (sudo does this for the service principal passed
to krb5_verify_init_creds()).  At least in the case of sshd there is an
explicit knob to turn this off.

However, this has made me wonder: why do this at all?  What is the
possible security gain here?  It's not the default in the code; you have
to explicitly write code to enable this behavior.  But I can't really
think of a case where NOT having strict acceptor checking is a security
problem; I could maybe squint and envision some kind of weird hosted
server setup where it might matter, but I'm not sure that is ever done
in the real world.  I will admit it is entirely possible I am missing
something; if I am, I'd sure like to understand what I am missing.

--Ken

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Why do "strict acceptor checking"? Ken Hornstein <kenh@cmf.nrl.navy.mil> - 2024-10-07 20:23 -0400

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